1. Field of the Invention
The present invention generally relates to a method for testing television systems, and more particularly to a method of testing both analog and digital color television systems to measure differential-phase and differential-gain at continuously variable average picture levels (APL) anywhere between ten percent and ninety percent.
2. Description of the Prior Art
The test procedures presently used for the measurement of differential-phase and differential-gain requires the use of three different signals applied in a predetermined sequence to five consecutive lines to achieve 10 percent, 50 percent and 90 percent APL. These procedures are set forth, for example, in "I. R. E. Standards on Television: Measurement of Differential Gain and Differential Phase, 1960," Proceedings of the I. R. E., Volume 48, No. 2, February 1960.
While these standards have been adequate for testing conventional analog television systems, they have several disadvantages. First, the test signals employed can not represents a selected APL on one line and are therefore not suitable for single-line testing. Second, since the test signals employed represent a selected APL by the combination of signals on several lines, there is a lack of line-to-line correlation. Thus, the prevailing I. R. E. Standards are not suitable for the testing of digital or other systems where correlation techniques are used. Finally, according to the I. R. E. Standards, only three fixed APL's are represented, namely, 10 percent, 50 percent and 90 percent.